1. Field of the Invention
A warning and control system for motor vehicle air conditioners.
2. Description of the Prior Art
Most motor vehicle internal combustion engines are cooled by means of a cooling liquid which is usually an aqueous solution containing a dissolved anti-freeze chemical such as ethylene glycol (permanent type) or methanol, and which circulates through the engine block and through a radiator. The radiator is located in front of an air fan disposed at the front of the engine block and driven by a belt mounted on a crankshaft pulley. As the engine crankshaft turns and especially when the vehicle is in motion, air is sucked inwards through the radiator and towards the engine by the fan, which air is initially at generally ambient temperature. The air, when directed through the fins of the radiator, cools the cooling liquid which is in constant circulation in series through the radiator and engine block as long as the engine is running. Thus, heat is transferred via the liquid cooling medium from the engine block (where gasoline combustion is taking place) to the air, and as a result, the engine block is cooled and not allowed to overheat.
The usual motor vehicle engine cooling system includes a pressure release safety valve, which opens to alleviate excessive pressure generated when the temperature of the cooling system liquid exceeds a predetermined level. The safety valve is provided because if the radiator is not properly cooling the cooling liquid, the temperature of the cooling liquid rises to inordinate levels and eventually a portion of the cooling liquid is converted to steam and/or vaporized antifreeze, with corresponding increases in pressure which could blow out gaskets and hoses, or rupture the hoses or even rupture the radiator. Thus, to prevent damage to the appurtenances of the engine, the pressure relief valve opens and safely discharges fluid from the cooling system, so that the pressure in the cooling system cannot exceed a safe level.
When overheating does occur, the steam and antifreeze vapor created by excessive heating of the cooling liquid eventually builds up to a pressure at which the pressure relief valve opens. The steam and/or antifreeze vapor thus escapes, and consequently some of the cooling liquid is lost. The overheating, being signalled by a warning light on the dashboard, which light is electrically connected to a heat sensitive switch that is mounted into the engine block or water pump, requires the motor vehicle driver to stop the motor vehicle and shut off the engine, raise the hood, or take other steps to allow the engine to cool. Then, before the engine of the motor vehicle can be again operated, it is usually necessary to add more cooling liquid from an external source, i.e. to supplement the body of residual cooling liquid in the engine with a fresh make-up supply. Very frequently, when the cooling system of a motor vehicle such as an automobile, bus or truck becomes overheated in summertime, a substantial amount of cooling liquid which may contain valuable antifreeze and antirust components is lost, and there is insufficient cooling liquid in the system, after the engine is cooled, to properly cool the engine. Thus, there is a three-fold problem with an overheated motor vehicle engine. First, it requires the need to shut off the engine. Second, it can lead to damage to the engine, especially if the pressure relief valve does not operate properly. Third, costly antifreeze and other components of the cooling liquid medium are lost and must be replaced, for safe wintertime operation. Recent advances in cooling system technology entail the provision of costly but effective packaged liquid coolant formulations which are not blended with water but instead are intended to be used per se at full strength.
The air conditioning of motor vehicles, especially of automobiles, trucks and buses, is much in demand by consumers and travelers, and many of them are factory equipped with an air conditioning system of well known design, which usually includes, inter alia, a compressor and a condenser. A control system for a motor vehicle air conditioner is described in my U.S. Pat. No. 3,904,885. The condenser is air-cooled by ambient air, and is usually located in front of the engine radiator. When the air conditioner is in service and the air conditioner compressor is operative, the refrigerant fluid such as a freon in the air conditioning system becomes heated, due to its function of absorbing heat from the interior body compartment of the motor vehicle, and consequently the temperature of the freon or other refrigerant fluid in the condenser increases. Therefore, the temperature of the cooling air passing in series through the fins of the condenser and the radiator rises, and instead of receiving ambient air as is the case when the air conditioning sytem is not functioning, the radiator receives preheated air. In other words, when the air conditioner compressor is running, the temperature of the condenser increases and thus the temperature of the cooling air increases from ambient as the cooling air flows through the condenser fins. Thus, the air, which is subsequently directed through the radiator fins, is preheated thus it cannot function efficiently as a cooling agent.
The operation of an air conditioning unit in a motor vehicle does not entail serious overheating problems when the motor vehicle is moving at a reasonable velocity, and large volumes of ambient air flow through the condenser fins, since the air temperature rise is minimized since the rate of heat removal is fairly constant. However, at low motor vehicle speeds and in hot weather, an overheating problem may be created relative to the motor vehicle engine in vehicles equipped with an air conditioner system, especially when the vehicle is traveling at a slow velocity or with stop-and-go driving, which generates heat in the engine at a very high rate since the inertia of the stopped vehicle must be overcome by the engine to place the vehicle in motion. This is commonly encountered in summertime traffic jams, in urban centers, or when a traffic stoppage occurs due to an accident or the like. What happens is that the air flowing through the condenser fins is heated, so that this heated air is directed through the radiator fins at an initially elevated temperature, and satisfactory heat dissipation from the cooling medium within the radiator cannot occur because of a relatively low temperature driving force (.DELTA.T) for heat transfer. Another adverse factor when the motor vehicle is not moving at substantial velocities is that there is a relatively reduced volumetric flow rate of air flowing through the radiator fins at slow motor vehicle velocities. Thus, the problem becomes compounded and overheating of the motor vehicle cooling system occurs. A factor in alleviating this overheating would be the temporary interruption of the operation of the air conditioner system, in particular the compressor, since this would lead to the provision of ambient rather than preheated air through the radiator fins.